1. Field of the Invention
The present invention relates to a container suitable for containing agricultural chemicals, fuel oil and industrial chemicals.
2. Description of the Prior Art
Heretofore, containers made of polyolefins such as polyethylene or polypropylene have been generally used for holding agricultural chemicals, fuel oil and industrial chemicals such as those of aromatic hydrocarbon series or aliphatic hydrocarbon series. These containers, however, are unsatisfactory because they swell or crack after a certain period of time in view of a poor resistance to chemicals so that they cannot be widely used from the viewpoint of safety.
In order to improve the chemical resistance of these containers, the use of a resin such as nylon having good resistance to organic chemicals has been proposed. Although such attempts to produce hollow containers made solely of nylon have been continuing for a considerable period of time, such containers have not yet been commercialized, because of various disadvantages and difficulties associated therewith such as the high cost of nylon, its poor moldability and drawdown owing to the low molten viscosity, and the low fused adhesion strength of the pinch-off portion in the bottom of such single layer nylon containers leading to an easy separation of the pinch-off portion if the container is dropped.
Therefore, contents such as agricultural chemicals, fuel oil and industrial chemicals have been generally held in metallic cans or glass bottles at the present time. However, disposal of wastes of metallic cans and glass bottles after use thereof has become a social problem. In place of these containers, containers suitable for filling such contents have long been desired.
As an example of a method of coping with those prior art problems is that shown in Japanese Patent Laid-Open Publication No. 53-21675 (1978), in accordance with which the production of a three-layer container having an excellent chemical resistance and moldability by the multi-layer co-extrusion blow molding method has now been developed and put to practical use. This three-layer container comprises an intermediate layer consisting of an adhesive polyolefin, and an inner layer, which is brought into direct contact with liquid contents, consisting of nylon or saponified ethylene-vinyl acetate copolymer having an excellent resistance particularly to organic solvents and so on. These resins, however, do not exhibit an excellent resistance to all liquid contents. For example, nylon is very poor in resistance to phenols, alcohols, strong acids and weak acids. The saponified ethylene-vinyl acetate copolymers have the defect that they do not have a sufficient resistance to solvents having a hydroxyl group as in the case of nylon. Metals are inappropriate for acids, and glass is inappropriate for alkaline hydrates.
A fluorocarbon resin is generally known as a material exhibiting an excellent resistance to all chemicals. The fluorocarbon resin is generally excellent in chemical resistance and has no water absorption properties, and its abrasion resistance, self lubrication and non-tackiness are the best among synthetic resins. Tetrafluoroethylene resin (hereinafter referred to as TFE) is the most well known of the fluorocarbon resins. TFE has the lowest chemical activity possible as a fluorine-containing polymer, and the lowest friction, non-tackiness, best dielectric performance, minimum water absorption, highest resistance to high and low temperatures and best weathering property among the fluorocarbon resins. However, TFE does not have a plasticity which permits it to be molten at its melting point, so that its processability is extremely poor. Accordingly, it is processed according to a method similar to that adopted in the field of powder metallurgy, and its use is therefore limited.
Thermoplastic fluorocarbon resin which are extrusion moldable may include ethylene-tetrafluoroethylene alternating copolymer resin (hereinafter referred to as ETFE), polyvinylidene fluoride resin (PVDF), polyvinyl fluoride resin (PVF), ethylene-ethylene chloride trifluoride alternating copolymer resin (ECTFE), polyethylene chloride trifluoride resin (PCTFE) and tetrafluoroethylene-hexafluoroethylene alternating copolymer resin (FEP). These resins contain fluorine atoms in their molecular segments so that they exhibit properties similar to those of TFE. Although the fluorocarbon resins have favorable properties, they are very expensive, so that their use is restricted to some special fields.
The thermoplastic fluorocarbon resins also have difficulty in laminating with other resins because they generally have significant non-tackiness.
In order to overcome these defects, we have disclosed in our copending Japanese Patent Laid-Open Publication No. 56-13337 (1981) a multi-layer co-extrusion blow molding method adapted to produce a container having a favorable chemical resistance, water-vaporproof, interlaminar strength and economy in production, the container comprising an inner layer made of a thermoplastic fluorocarbon resin, an intermediate layer made of a polyolefin grafted with an unsaturated glycidyl compound, and an outer layer made of a polyolefin. This method, however, has the defect that it has a poor co-extrusion blow moldability although the interlaminar strength is satisfactory. In this method, the fluorocarbon resin to be used as the inner layer has a high molding temperature ranging from 250.degree. to 350.degree. C., so that the molten viscosity of the unsaturated glycidyl graft-modified polyolefin as the intermediate layer to be extruded as a laminate with the fluorocarbon resin decreases remarkably, leading to irregularities in the wall thickness of the inner and intermediate layers in the circumferential direction of the resulting container. In some extreme cases, the graft-modified polyolefin for the intermediate layer cannot be filled to form a full intermediate layer, resulting in a container wherein the thermoplastic fluorocarbon resin and the polyolefin are locally separate from each other.